Extrusion apparatus



April 5, 1966 D. GREEN 3,243,985

EXTRUSION APPARATUS Filed Sept. 28, 1964 United States Patent 3,243,985 EXTRUSION APPARATUS Derek Green, Lytham St. Annes, England, msignor to United Kingdom Atomic Energy Authority, London, England Filed Sept. 28, 1964, Ser. No. 399,564 2 Claims. (Cl. 72-260) This invention relates to extrusion.

Extrusion of the kind in which a workpiece of metal is driven through a die to form a continuous strip or bar of material having cross-sectional shape similar to that of the orifice in the die is well known. One application of this kind of extrusion is in the manufacture of fuel elements for nuclear reactors. It is known to extrude a uranium bar having a zirconium sheath through a die to effect intimate contact between the bar and sheath. My copending British application No. 48048/62 describes a method and apparatus for forming a nuclear reactor fuel element by compacting fissile material of particulate form in a metallic sheath by hydrostatic extrusion through a die. But, in each of the foregoing applications, the penalty of considerable frictional resistance between the workpiece and die has to be accepted and in the case of some materials, zirconium for example, the result is a poor surface finish caused by galling. Extrusion can be facilitated and surface finish improved by coating the workpiece with a tenacious, deformable material such as latex as described in the aforementioned application, the coating serving to prevent physical contact of the Workpiece with the die during extrusion.

According to the invention, extrusion apparatus has a resiliently yieldable non-metallic die and means for deforming the die radially inwardly during extrusion of a workpiece therethrough to urge the throat of the die into close embracement of the workpiece.

Preferably, the die is made from nylon or polytetrafiuoroethylene and the means for deforming the die radially inward into close embracement of the workpiece is fluid pressure means. Such fluid pressure means may, in the case of hydrostatic extrusion, be derived from the fiuid pressure means employed to drive the workpiece through the die.

An embodiment of the invention will now be described, by way of example, with reference to the sole figure of the drawing which is a fragmentary sectional side view of a part of an apparatus suitable, inter alia, for forming nuclear reactor fuel elements by compacting particulate fissile material, for example uranium dioxide, in a nonfissile sheath, for example stainless steel, by an extrusion process.

A container 1 is adapted to be pressurised hydraulically and houses a die holder 2 having a die 3 made of nylon. A pressure intensifying piston 4 has an annular face 5 at one end and a smaller annular face 6 at the other and a workpiece 7 (which comprises a fuel element workpiece 3,243,985 Patented Apr. 5, 1966 of composition hereinbefore described) is threaded coaxially through the assembly. A rubber O ring 8 provides a glanded seal for the piston 4 and a duct 9 affords a vent to atmosphere for the annular void bounded by the piston and die holder 2.

In use the container is pressurised so that the workpiece '7 is hydrostatically supported as it enters the die 3 and is forced through the die by pressure on its end face. Fluid pressure on the annular face 5 is intensified by the smaller area of the annular face 6 which bears on the face of the die 3 which die, being constrained by the holder 2, is deformed radially inwardly during passage of the workpiece therethrough.

The apparatus has advantage in that frictional resistance between the die and workpiece is reduced thus easing passage of the workpiece therethrough with consequent improved surface finish and little wear on the die. Within limits, wear on the die is compensated for by radial deformation of the die.

I claim:

1.. Extrusion apparatus for use in hydrostatic extrusion of a workpiece by pressurization of hydraulic liquid about the workpiece in an extrusion chamber, comprising means forming an extrusion chamber, an extrusion die assembly located at one end of the extrusion chamber, said extrusion die assembly comprising a die of resiliently yieldable material contained in a close fitting cup-shaped housing of nondeformable material, the inner end face of the die facing the interior of the extrusion chamber at the open end of the cup-shaped housing, and means for transmitting pressure from the liquid pressure applied on the workpiece in the extrusion chamber to the inner end face of the die in the cup-shaped housing so that the die is compressed longitudinally in the housing and thereby deformed radially inwardly about the workpiece during extrusion.

2. Extrusion apparatus as set forth in claim 1 wherein said means for transmitting pressure comprises a piston slidably sealed in the bore of the extrusion chamber and having an extension of smaller diameter entered into the open end of the cup-shaped housing, the rear face of the piston being subjected to the pressure of liquid in the extrusion chamber, and the front face of the extension of the piston bearing against the inner end face of the die in the housing to apply deforming pressure on the die.

References @ited by the Examiner UNITED STATES PATENTS 3,021,003 2/1962 Bluck 207l8 3,134,832 5/1964 Smith 207--18 FOREIGN PATENTS 476,793 9/1951 Canada.

CHARLES W. LANHAM, Primary Examiner.

E. D. OCONNOR, Examiner. 

1. EXTRUSION APPARATUS FOR USE IN HYDROSTATIC EXTRUSION OF A WORKPIECE BY PRESSURIZATION OF HYDRAULIC LIQUID ABOUT THE WORKPIECE IN AN EXTRUSION CHAMBER, COMPRISING MEANS FORMING AN EXTRUSION CHAMBER, AN EXTRUSION DIE ASSEMBLY LOCATED AT ONE END OF THE EXTRUSION CHAMBER, SAID EXTRUSION DIE ASSEMBLY COMPRISING A DIE OF RESILIENTLY YIELDABLE MATERIAL CONTAINED IN A CLOSE FITTING CUP-SHAPED HOUSING OF NONDEFORMABLE MATERIAL, THE INNER END FACE OF THE DIE FACING THE INTERIOR OF THE EXTRUSION CHAMBER AT THE OPEN END OF THE CUP-SHAPED HOUSING, AND MEANS FOR TRANSMITTING PRESSURE FROM THE LIQUID PRESSURE APPLIED ON THE WORKPIECE IN THE EXTRUSION CHAMBER TO THE INNER END FACE OF THE DIE IN THE CUP-SHAPED HOUSING SO THAT THE DIE IS COMPRESSED LONGITUDINALLY IN THE HOUSING AND THEREBY DEFORMED RADIALLY INWARDLY ABOUT THE WORKPIECE DURING EXTRUSION. 